The present invention relates to a metal gasket having a sealing device with different spring constants. In particular, the spring constant of a sealing device, such as a bead, for sealing around a fluid hole of an engine is partly changed to securely seal around the fluid hole.
In a metal gasket, such as a steel laminate gasket for a cylinder head, cylinder bores, water holes, oil holes and so on are sealed by beads and/or other sealing devices. Especially, since the metal is durable and can be processed easily, the holes are liable to be sealed by only metal processing, i.e. bending the metal to form beads and so on.
In the cylinder head gasket, high pressure and temperature are applied to the cylinder bores, so that the area around the cylinder bore is liable to leak. Therefore, bolts for attaching the gasket to the cylinder head and cylinder block are arranged to effectively seal around the cylinder bores to prevent leakage therefrom.
The cylinder head gasket includes the water holes, oil holes and so on as well as the cylinder bores. Although sealing pressure is effectively applied to the cylinder bores, sealing pressure is not equally applied to other holes due to location of the hole. Therefore, it is difficult to effectively seal around all the holes, such as the water holes and oil holes. In long usage, sealing ability decreases to cause leakage from these holes.
In order to compensate unequal sealing pressure by tightening of bolts, it was proposed to form an auxiliary bead at a portion where tightening pressure is low, as disclosed in U.S. Pat. No. 4,759,556. Namely, main and auxiliary beads provide high spring constant at a low tightening pressure portion.
In Japanese Patent Publication (KOKAI) No. 62-261755, the width of a bead is changed such that a center between the bolts becomes narrow. As a result, spring constant in the center portion between the bolts becomes high.
In Japanese Utility Model Publication (KOKAI) No. 60-177371, a bolt hole is surrounded by an outer bead with different spring constant. Namely, an inner portion of the bead around the bolt hole is stronger than an outer portion of the bead around the bolt hole, while the bead between the two bolt holes is the strongest.
The prior art patents disclosed that spring constant of one bead is changed to provide high spring constant at a low tightening pressure portion. However, there is no disclosure for sealing around a fluid hole adjacent the cylinder hole.
Accordingly, one object of the present invention is to provide a metal gasket, which can securely seal around a fluid hole adjacent a cylinder hole of the engine.
Another object of the invention is to provide a metal gasket as stated above, which can equally provide sealing pressure around the fluid hole of the engine.
A further object of the invention is to provide a metal gasket as stated above, which can be manufactured easily and economically.
Further objects and advantages of the invention will be apparent from the following description of the invention.